Coal-fueled diesel engines must achieve complete combustion of the coal fuel within a limited residence time. Complete combustion is essential to achieve desired engine performance and to reduce degradation of the engine and the environment. The ability to intermittently inject, ignite, and burn coal fuel in a diesel engine is primarily a function of the particle size and chamber residence time. The relative influences of chamber geometry, fuel characteristics, and changes in engine load on the coal particle burnout must be considered in order to maximize the burning process. However, particle agglomeration, ignition, flame development, particle burnout, emissions, and combustion efficiency are parameters affected not only by the fuel, but also the method of injecting the fuel into the engine.
Coal-based fuels currently under use are generally in the form of a coal slurry, that is, a mixture of coal particles in an approximate 50/50 mixture with water. Solid coal particles have also been used, as well as a vaporous mix of coal particles and steam, etc.
One of the major drawbacks to the use of coal-based fuel in diesel engines is the degradation of engine performance caused by coal itself and contaminants. This problem originates with the coal, the ash and unburned coal particles passing through the engine, causing accelerated wear on the injector systems, particularly on injector spray holes. In addition, these particles cause premature wear on cylinder walls, rings, valves, and exhaust components. As the injector spray holes, valve seat, and plunger erode away and change in size and shape, the direction of the fuel as it is injected into the chamber is changed. In some cases, the fuel is directed onto the piston, where a hole can subsequently be burned on the piston. In addition, plugging of the injector can result as water separates from the coal.
One proposed method of overcoming these disadvantages is to use high-pressure air to blow the solid coal particles into the combustion chamber. The difficulty here is that pneumatic pump lubricating oil tends to mix in with the high-pressure air or fuel that migrates back into the high-pressure air lines, causing serious damage or destruction of the engine. The present invention is directed to overcoming these drawbacks.